Super late reply, apologies. On this https://man.sr.ht page, giving .event items 1rem padding reduces crowding and makes the elements. Start doing that to the other elements as well, pre, etc. They should all be the same so the gutters are the same.
Setting .btn padding to .5rem .75rem balances the hight of the type vs. the edge of the button a bit, making the buttons both more 'substantial' and moving the harsh btn edge away from the type, which makes it easier to read.
Add margin-top 2.5rem to your h* elements to space your content out.